The type and magtude of loads that pass through the track superstructure have a great impact on both the design and the performance of the concrete crossties and fastening systems. To date, the majority of North American research that focus on quantifying the rail infrastructure loading conditions has been conducted on heavy-haul freight railroads. However, the results and recommendations of these studies may not be applicable to the rail transit industry due to a variety of factors. Unlike the freight railroads, which have standardized maximum gross rail loads and superstructure design practices for vehicles, the rail transit industry is home to a significant variety of vehicle and infrastructure designs. Some of the current transit infrastructure design practices, which were established decades ago, need to be updated with respect to the current loading environment, infrastructure types, and understanding of the component and system-level behavior. This study focuses on quantifying the current load environment for light rail, heavy rail, and commuter rail transit infrastructure in the United States. As an initial phase of this study, researchers at the University of Illinois at Urbana-Champaign (UIUC) have conducted a literature review of different metrics, which is used to evaluate the static, dynamic, impact, and rail seat loads for the rail transit infrastructure. UIUC will compare these methods and their computed values to determine which provide the most accurate depictions of the expected loading condition given a set of operating and infrastructure characteristics. A proper load quantification of rail transit systems, gained through an improved understanding of the load path and rail seat load, will help to establish the basis for developing recommendations for a mechanistic design process for the rail transit infrastructure components. Ultimately, the results of this research will allow transit agencies to increase the effectiveness of their capital spending and transit agencies will have the potential to improve safety, ride quality, capacity, and the life cycle of the rail transit infrastructure.